Rocket Launch-to-Orbit Model

The rocket model accepts rocket parameters such as payload and fuel mass, and calculates the rocket's launch trajectory. The model is useful for optimizing the parameters to reach specific orbits. This model is part of CSIM's Vehicles/Platforms/Terrains (VPT) model library.

An intuitive control panel interface, pictured in Figure-1 below, assists in setting parameters, running optimizations, and visualizing results.

The following parameters are available from the control panel:

Payload Mass - In Kilograms (Kg).
Fuel Burn Rate (Kg/Sec) and Burn-duration per stage (Secs) - These are used to calculate the initial fuel-load mass, and changing mass during flight.
Exhaust Velocity (m/sec) - Used with above burn-rate to calculate the rocket's thrust. Value depends on the fuel type, engine and nozzle design.
Overhead-Mass Factor - Ratio of the non-fuel and non-payload mass, to total mass. This accounts for the rocket structure that is not part of the reaction mass, such as engines, tanks, fairings, and first-stage casing.
Cross Section Area (m^2) and Drag Coefficient - to calculate aerodynamic drag while in the atmosphere. These are properties of the rockets shape and size, especially in the nose-cone area.
Pitch rate (Deg/Sec) - By default, the initial model assumes the rocket launches vertically, and pitches at a regular rate until tangential to Earth's surface in circular orbit. The model can be easily modified to deliver more complex pitch profiles.
Apogee Kick Duration (Secs) - By default, model assumes a main burn to reach velocity, coast to desired altitude, and an apogee kick burn to circularize the orbit. The model can be easily modified to deliver more complex thrust and vectoring profiles.

Additional parameters are available within the model-code. This model is based on classic Newtonian mechanics, with all units in MKS-SI units (Meters, Kilogram, Seconds - System International). Plot outputs are available in English units as well. One purpose of this model is to serve as a starting-point, or example, for how to make more complex models of rocket vehicles. One value is that all the relevant constants and functions are pulled together in one spot (ex. Earth's mean radius, non-rotational gravitational acceleration, air density and drag versus altitude, gravitational force versus altitude, Earth's rotational speed versus latitude, etc.). The base model can be used to solve for the best trajectory to minimize fuel, the best combination of engine parameters, burn-time, and burn rate for a given payload, or even to optimize re-entry maneuvers.

Usage:

To use the rocket model, open CSIM's GUI and click File / Open New File. Click the check mark next to the file entry box. Select $CSIM_MODEL_LIBS, and press OK. Navigate into the vpt / vehicles directory, and select rocket.sim. A diagram with two boxes should appear.

Build a textual (non-graphical) simulation by clicking: Tools / Modify-Commands / Build Textual-Sim. You are now ready to run simulations. You can exit out of the drawing GUI.

Invoke the Launch-Control panel by typing: launch_controller
The tool pictured above will open.

There are several ways to use the Launch-Control panel. The simulation model can also be run directly, or through over means. This discussion continues assuming usage of the Launch-Control panel, which is a convenient way to become familiar with the model.

The simplest way to use the Launch-Control panel is to type your desired values into the entry boxes. Once you have set the values, click the Simulate button. The model will accept your new parameters, the simulator will run, and the results will be plotted in the lower graphs. You can see more detailed plots by clicking the Plots button at the top.

Another way to use the Launch-Control panel is to directly adjust the parameters with the slider controls. As you adjust the parameters, the simulation will run and you will see the results immediately in real-time. (CSIM runs very fast.)

Once you have your basic parameters near their intended ranges, you can automatically optimize the remaining parameters to achieve a highly circular orbit, by clicking the Optimize button. During optimization, the plots are updated periodically to view progress. You can set the number of iterations to optimize over, for each click of the Optimize button, in the field to the left of the slider. This option merely runs CSIM's Iterator tool, by setting up an iterator.control file. You can easily customize and extend this file and process, according to your project needs. Please contact CSIM for support or training, if needed.

Detailed plots can be obtained at any time by pressing the Plot button at the top of the screen, as shown in the figure below:

Additional plots can be obtained by adding your own fprints to the model.

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